The NHS/private divide — and why it shapes your choices

For most people with knee osteoarthritis, the first question is a practical one: can I get a single-injection treatment on the NHS? The short answer is partly. The NHS will offer a corticosteroid (steroid) injection when first-line measures — exercise, physiotherapy, and weight management — have not brought sufficient relief. That is where NHS intra-articular provision stops. Every advanced single-injection formulation discussed below sits firmly in the private sector.

The reasons are regulatory and evidentiary rather than arbitrary. NICE has published formal guidance on only one advanced injection type for knee OA — platelet-rich plasma (reference HTG497) — and even that does not translate to routine NHS commissioning. Arthrosamid® (polyacrylamide hydrogel) was reviewed under NICE reference GID-MT606 and recorded as 'not selected' for Health Technology Evaluation, citing insufficient evidence. Single-dose hyaluronic acid and autologous protein solution have not reached equivalent NICE assessment stages. The practical consequence: a treatment available at a reputable private clinic is not the same as a treatment recommended by NICE or commissioned by NHS England.

Private access does not mean unregulated. These treatments are delivered by musculoskeletal specialists in regulated clinical settings, and the evidence behind each varies considerably in depth and design. Costs run from approximately £400 to over £3,000 per injection depending on the product, provider, and whether an initial specialist consultation is included.

'Single injection' is a scheduling description, not a clinical category — and that distinction has real consequences. The four options below differ in mechanism, durability, evidence base, and the stage of OA they are designed for. Understanding those differences is the starting point for any informed decision.

Corticosteroid injection — the NHS starting point

Steroid injections work by delivering a corticosteroid — typically triamcinolone or methylprednisolone — directly into the synovial space, where it suppresses local inflammatory activity. The result is usually rapid: many patients notice meaningful pain reduction within days. That speed makes corticosteroid injection genuinely useful when an inflammatory flare is the dominant symptom, regardless of underlying OA severity.

The limitation is durability. Relief typically lasts weeks to a few months rather than years, and the injection addresses inflammation rather than the underlying cartilage loss driving the condition. Repeated use is not a neutral option: evidence suggests that frequent corticosteroid injections may accelerate cartilage degradation over time, and most clinical guidelines advise limiting the number of courses per year. Patients with diabetes should also be aware that intra-articular steroids can cause a transient glycaemic spike, which warrants appropriate monitoring.

For many patients with mild-to-moderate OA, a corticosteroid injection provides a useful period of symptom control — creating a window for continued physiotherapy or structured exercise. Where symptoms are driven more by chronic structural change than by acute inflammation, however, its short duration becomes a more significant clinical constraint.

Arthrosamid — the polyacrylamide hydrogel option

Of the advanced single-injection options available in UK private practice, Arthrosamid® carries both the longest marketed relief duration and the most scrutinised regulatory history.

The product is a 2.5% polyacrylamide hydrogel (PAAG) administered as a single ultrasound-guided intra-articular injection. Unlike treatments that are absorbed or metabolised over time, PAAG integrates with the synovial tissue lining the joint, where it acts as a durable mechanical cushion. The manufacturer cites relief of up to three years — which, if borne out in further evidence, would meaningfully exceed the durability of single-dose hyaluronic acid or autologous protein solution. Patient selection matters: Arthrosamid is indicated for moderate-to-severe knee OA, not for early-stage disease or focal cartilage defects.

The evidence picture is genuinely mixed. A Cole et al. (2022) systematic review reported statistically significant efficacy at 52 weeks and 13 months, with numerically superior outcomes compared to hyaluronic acid — encouraging data, though constrained by the absence of long-term randomised controlled trials. NICE assessed Arthrosamid under reference GID-MT606 and recorded it as 'not selected' for Health Technology Evaluation, citing the evidence base as insufficient. It is worth being precise about what that means: 'not yet enough evidence' is a different conclusion from 'does not work', and the question remains open. The NHS-linked research study that might have addressed that gap has since closed recruitment.

Access across UK private practice is well established. Circle Health Group, Nuffield Health, Imperial Private Healthcare, Benenden Hospital, and Pure Sports Medicine all offer the injection; in January 2025 Pure Sports Medicine announced a partnership with Contura Orthopaedics to expand clinic availability further.

nSTRIDE APS — the autologous protein option

Unlike the hydrogel options that work mechanically, nSTRIDE® APS operates at the level of the joint's chemistry — specifically the inflammatory signals that accelerate cartilage breakdown in OA.

The treatment is produced from the patient's own blood. A bedside centrifuge processes a small draw to concentrate two groups of proteins: anti-inflammatory cytokines (interleukin-1 receptor antagonist, IL-1ra, and soluble tumour necrosis factor receptor, sTNF-R) and anabolic growth factors (IGF-1 and TGF-β). In a healthy joint these signals are roughly balanced; in OA, the destructive cytokines dominate, suppressing the repair signals the joint needs. The concentrated solution is then injected in a single dose to counteract that imbalance. Because the solution is drawn from the patient's own blood, there is no donor tissue and no synthetic material involved.

nSTRIDE is indicated for mild-to-moderate knee OA — a meaningfully different patient selection from Arthrosamid, which targets moderate-to-severe disease. UK providers cite trial data reporting a 70% improvement in knee pain at two years following a single injection; it is worth noting that this figure is quoted from clinical trials cited by providers rather than from an independently published RCT. Typical quoted relief sits at 6–12 months, which is shorter than the three-year claim associated with polyacrylamide hydrogel and should be factored into decision-making. No head-to-head trials comparing nSTRIDE to Arthrosamid or single-dose hyaluronic acid currently exist.

The treatment is available at several UK private clinics — including Nuffield Health, London Orthopaedic Clinic, DC Knee, and Pro Sports Medicine in Wales — but sits outside both NHS commissioning and NICE guidance.

Single-dose hyaluronic acid and PRP — the established private options

Two treatments sit at the more established end of the UK private injection landscape: single-dose hyaluronic acid — most commonly Monovisc® — and platelet-rich plasma (PRP). Both are widely available in private practice; neither is routinely funded on the NHS.

Monovisc — single-dose viscosupplementation

Monovisc delivers 88 mg of ultra-pure, non-avian hyaluronic acid in a single injection. The aim is to supplement the degraded synovial fluid of an arthritic knee, restoring some of its natural lubricating and shock-absorbing properties. Relief is typically quoted at up to six months — shorter than the duration claims associated with the polyacrylamide hydrogel described in the previous section.

The evidence base is contested on two fronts. A systematic review of 11 studies found no consistent difference in patient-reported outcomes between single and multiple HA injection courses. An earlier meta-analysis pressed the point further: 2–4 injection regimens and courses of five or more injections both outperformed saline, but single-injection HA did not. This is a genuine finding in the literature, not a marginal one, and any honest comparison should acknowledge it. Individual responses vary, and some patients report meaningful relief — but the class as a whole lacks the clean evidence profile that would distinguish it from an active placebo in all comers. Viscosupplementation is explicitly not normally funded on the NHS.

PRP — the only option with formal NICE guidance

PRP holds a distinct position among the treatments in this group: NICE has published formal guidance on it for knee OA, under reference HTG497. That is not equivalent to a commissioning recommendation or NHS funding, but it represents a level of national regulatory scrutiny that none of the other advanced single-injection options covered here has reached.

The mechanism differs from both HA and polyacrylamide hydrogel. PRP is drawn from the patient's own blood and concentrated to deliver a high dose of platelets, which release signalling proteins — including platelet-derived growth factor and TGF-β — that may support the joint's own repair environment rather than providing direct mechanical lubrication. NICE's evidence review examined single-injection protocols, including leukocyte-reduced preparations of approximately 4 mL given in a single dose. Published series in that evidence base report variable outcomes; some trials found clinically meaningful reductions in pain sustained at 12 months in patients with mild-to-moderate OA, though the spread of results across studies is wide. PRP is available across multiple UK private clinics and, where delivered as a single injection, fits the treatment format this article addresses.

Which option suits which patient

Choosing between these options is not straightforward, and the evidence base does not yet support a patient self-selection checklist. That said, certain population-level patterns emerge from the clinical positioning of each treatment.

OA severity is the clearest sorting variable:

• Mild-to-moderate OA — nSTRIDE APS is specifically indicated here; single-dose HA and PRP also sit comfortably in this range.
• Moderate-to-severe OA — Arthrosamid's positioning is explicitly at this end of the spectrum; corticosteroid remains relevant for inflammatory flares at any severity.

Duration of relief shapes priorities differently depending on what a patient is managing:

• Short-term (weeks to months): corticosteroid, single-dose HA
• Medium-term (6–12 months cited): nSTRIDE APS
• Longer-term (up to 3 years marketed): Arthrosamid

Symptom character provides a further steer: inflammatory flare pain points toward corticosteroid or PRP; mechanical load-related pain may favour viscosupplementation or hydrogel.

Crucially, no published head-to-head RCT compares Arthrosamid, nSTRIDE, single-dose HA, and PRP directly. The patterns above are derived from each product's separate evidence base and clinical positioning — not from comparative trials. Individual suitability also depends on imaging findings, body weight, prior treatment history, and what the patient is trying to achieve, none of which a general summary can resolve.

The most productive next step for anyone working through these options is a structured conversation with a musculoskeletal specialist — armed with the severity-and-mechanism framework this article has outlined. That conversation should cover which treatment tier fits the current OA stage, what outcome is being targeted, and what the realistic trade-offs are given the individual's history.